1. Field of the Invention
This invention relates to anchors and bolts used to secure plates and framing of a building to its foundation and/or slab, and in particular to the setting of anchor bolts or hold down bolts, and/or re-bar, after forming, but before the placement of concrete.
2. Description of Prior Art
Hand-set Bolts
The usual way that a foundation or slab floor of a building is constructed is to build perimeter formwork to contain the wet concrete to be poured. Steel in the form of re-bar is placed within this formwork. A wet unset concrete mixture is poured into the area contained by the formwork and the top edge of the formwork is used as a guide for determining the level of this concrete.
Anchor bolts or hold down bolts, which are both steel rods of varying length and diameter, are incorporated into this concrete. Each bolt, usually threaded at one end, is placed so that this threaded end projects vertically from the concrete of the slab or footing. A portion of the part of rod remaining in the concrete is usually bent perpendicularly or into some other configuration to increase its pullout resistance. After the concrete has hardened, a plate or mudsill of wood or metal is marked to locate each bolt position. These locations are then drilled. The plate is placed over the protruding bolt ends, and is tightly secured by nuts and washers fastened to these protruding bolt ends. It is this connection which secures a building to its foundation. The usual method of incorporating these bolts into the foundation is accomplished by having a worker hand set them in the wet concrete after the concrete has been screeded level.
Concrete foundations and slabs are also constructed using a two pour method of concrete foundation construction. With this method, concrete for the perimeter footing is poured first, its top level being about four inches lower than the level of the finished slab. After this concrete has hardened, a new mix of concrete for the slab is poured, covering this footing and filling the formwork to its finished level.
A problem with hand setting bolts in wet unset concrete, is the difficulty of maintaining standards of accuracy in the positioning of these bolts. One reason for this difficulty is that time is usually in short supply between the start of placement of the concrete and the steel trowel finishing of the surface of the concrete. Therefore, there is not extra free time to be devoted to the exact placement of bolts. Another reason for this difficulty is that often the least experienced worker on the job is the worker doing the placement. He may not have the training or experience necessary for the understanding of the importance of maintaining placement standards. Maintaining these standards is also difficult as at times the concrete does not have sufficient body to support the position of a placed bolt.
When these standards are not maintained, several costly consequences will result. Should the threaded end of the bolt not protrude sufficiently to allow its passage through the thickness of a mud sill, time and effort must be spent on chiseling out around the bolt hole through the sill. If the protruding bolt is out of plumb, its shaft may need to be bent back to vertical, damaging the bond of the bolt to the concrete, or weakening the shaft of the bolt.
Another problem with hand setting bolts, is that bolt location cannot be inspected before the placement of concrete. An insufficient number of bolts may be placed requiring the expensive addition of drilled and placed bolt systems. Also bolts may be placed at incorrect locations requiring their time consuming removal at a later date.
A further problem with the hand setting method is that the shaft of the bolt may not have a tight connection to the concrete. This occurs when the concrete of a slab has set to a point where it is no longer fluid and a void is formed around the shaft of a bolt forced into it.
Pre-set Bolts
To solve some of the aforementioned problems, contractors and inventors have resorted to several different methods to preset their bolts. One of these methods is created by drilling a hole in a board to accept the threaded top of a bolt. The bolt is pushed through this hole and a nut is threaded on to the bolt. This board is then nailed to the top of the form board, hanging the bolt into a position so that its threaded end will be free of, and its other end will be covered by the placed concrete. The board itself is positioned to be above the surface of the concrete. Once the concrete has hardened sufficiently to hold the bolt into position, the nails holding the board to the form board are removed, the nut holding the bolt to the board is removed, and the board is removed from the shaft of the bolt protruding from the concrete. There is a plastic hanger that has been manufactured, that holds and suspends a bolt in basically this same way.
One of the drawbacks with this method of setting an anchor bolt is that the bottom of the anchor bolt or hold down is not secured so that during the placement of the concrete the shaft of the bolt is often knocked out of plumb. Another problem with this method is that fastening the anchor bolt to the holder is a time consuming activity. Another problem with this method is that the hanger device must be removed after placement of the concrete in order to finish the concrete under it and this is a time consuming activity. A further problem with this method is that the hanger devices must be cleaned and carried from one job to another. Another problem is that a certain number of these devices break during use and new ones must be bought in order to maintain a sufficient inventory.
Embossed and bent sheetmetal mudsill anchors, such as is found illustrated in Gilb (U.S. Pat. No. 4,413,456), are manufactured by several companies. These are set by nailing to a form board before the placement of concrete. Each one is positioned so that about one-half of its length will be buried and held by the to-be-placed concrete. The other half remains free of the concrete. After the concrete is placed and hardened, this free section of strapping is disconnected from the form board, bent up and over the mudsill, and is nailed to the mudsill. With this device the mudsill cannot be torqued down as can be done with the nut and bolt arrangement of the anchor bolt. Because of this it is not as popular with contractors as the anchor or hold down bolt.
Re-bar Placement
In concrete construction re-bar is used to add to the structural strength of the concrete slab or footing. The re-bar used in concrete construction has certain placement requirements in order for it to be most efficient in this. Correct placement is also necessary to insure that sufficient concrete covers the re-bar protecting it from the oxidative effects of contact with water. Among the several ways to position re-bar before the placement of concrete is to hang it using tie wire that is attached to the form board. This method is time consuming and does not result in very accurate placement of the re-bar. Re-bar also is positioned by setting it on the ground inside the formed area and pulling it into position during placement of the wet concrete mixture. The concrete mixture then holds it in place. This method does not allow for inspection of the final positioning of the re-bar before the concrete placement.
Re-bar can also be placed in position using the sheetmetal mudsill anchor. This anchor contains a re-bar seat at its end that will be buried within the concrete. A problem with this device is that a blow to the re-bar holder or the re-bar can cause detachment of the anchor from the form board. As previously mentioned, most contractors do not like to use mud sill anchors.
Another device that is used to place re-bar is a hanger that is formed from bent wire. Such a device is illustrated in Frost (U.S. Pat. No. 5,042,218). The problem with this device is that it is prohibitively expensive.